I was told I need to run my poweramp in bridged mono but when I do that I get lots of pops and buzzing noise. I'm not sure i'm doing something wrong or if the poweramp is broke? My pod global settings are all correct with the stacked power amp setting etc. Any help would be appriciated as its getting rather annoying.

*Works perfect when its in stereo and only one speaker cable going to my cab.

Not sure the HD is the issue here. You might want to check out the manual for the Velocity regarding cab ohmage and stereo requirements. Stereo = two loads for the power amp, bridged = single load. Cab specs should match what is required.

From my old trusty Velocity 120 I know that when it would start to overheat the thermal protection would begin to make the sound start to distort.